The prevention of lowered contrast and lowered visibility caused by external light reflection or image reflection is required of image display devices, for example, cathode-ray tube display devices (CRTs), plasma displays (PDPs), electroluminescent displays (ELDs), or liquid crystal displays (LCDs). To meet this demand, it is common practice to provide a reflection preventive laminate on the outermost surface of an image display device from the viewpoint of reducing image reflection or reflectance using the principle of light scattering or the principle of optical interference.
When a reduction in image reflection or a reduction in reflectance utilizing the principle of optical interference is contemplated, a layer having a higher-refractive index and a layer having a lower refractive index than the higher-refractive index layer are generally stacked on a light transparent base material. In the optical laminate comprising layers, which are significantly different from each other in refractive index, stacked on top of each other, however, interface reflection and interference fringes often occur in the interface between the mutually superimposed layers. In particular, it has been pointed out that interference fringes are significant in the reproduction of a black color on the image display surface of an image display device and, consequently, the visibility of the image is lowered and, at the same time, the appearance of the image on the image display surface is deteriorated. In this connection, it is said that, when the refractive index of the light transparent base material is different from the refractive index of the hard coat layer, interference fringes are highly likely to occur.
Japanese Patent Laid-Open No. 131007/2003 proposes an optical film characterized in that, in order to suppress the occurrence of interference fringes, the refractive index around the interface of the base material and the hard coat layer is continuously changed.
So far as the present inventors know, however, any optical laminate has not been proposed in which the interface between the light transparent base material and the hard coat layer has been substantially eliminated.